1. Field of the Invention
The invention relates to the technical field of the inspection or scanning of a mark made in or on a transparent or translucent object. In one non-exclusive application, the invention relates to the scanning of two-dimensional codes such as Datamatrix codes etched or marked on the surface of receptacles or containers made of glass passing at a high speed in an in-line inspection system.
2. Description of the Related Art
Traceability in the glass industry is an increasingly strong constraint. Glass articles follow an increasingly complex manufacturing, distribution and filling process with numerous temporary storages and flow disruptions. Furthermore, the regulations stipulate having a capability to trace, through all the steps of manufacture, processing, distribution, routing of a food container by means of an identification enabling the traceability of the container. In order to meet this obligation, the glass industry has developed a hot marking technique making it possible to etch by means of a laser an individual identification mark specific to each container on a production line whereon the containers are produced at rates that may be between 50 and 600 articles per minute. The identification mark is presented for example in the form of a Datamatrix. In order to guarantee the effectiveness of such a traceability marking, it is necessary to ensure that the marking of each product is legible. For this purpose, it is necessary to scan the marking after the application thereof and cooling of the container at a rate compatible with the production rate so as not to create an accumulation point of the products and to be able, on one hand, to remove the containers wherein the marking is defective without delay and, on the other, record in a database the containers for which the marking is operational. The need for scanning at a high speed is also observed on filling lines in particular.
EP 2 164 028 discloses a system for inspecting code inscribed on the surface of glass receptacles intended for the pharmaceutical or chemical industry. As shown in FIGS. 5 and 6 of this published application, use is made therein of a point type lighting system focused on the code to be scanned so as to maximise the intensity of the signal received by the camera. The drawback of this optical system is that it is not suitable for compensating for the curvature of the glass surface. Indeed, if the code is situated on the edge of the glass article, the light will be deflected onto the sides and will escape the field of the camera. The usable inspection field is thus extremely limited to the centre of the product. Furthermore, the intensity of the signal received will be dependent on the angular position of the code in relation to the source and the acquisition device. Furthermore, the lighting system proposed is not suitable for adapting to different product diameters. Moreover, the optical system shown in FIG. 9a of the same document is an optical system with a single-lens camera. It collects all the reflective or incident rays in the lens without distinction.
As such, the inspection device disclosed in EP 2 164 028 is suitable for scanning code such as Datamatrix codes on good-quality glass intended for the fine chemical or pharmaceutical industries which has even wall thicknesses, smooth walls and no inclusion or surface defect. On the other hand, the device according to EP 2 164 028 is not suitable for scanning code on the surface of receptacles made of “rough” glass such as recycled glass used for the manufacture of food receptacles. Indeed, the inner and outer surfaces of such a receptacle may have numerous defects in respect of shape, glass distribution, inclusions in the glass matrix and skin liable to deflect the incident beam in the acquisition optics and generate a parasitic signal that the optical system according to EP 2 164 028 will not be able to filter. Similarly, glass skin defects such as wrinkling, seeding, grease stains may be superimposed on the signal within the code and will not be filtered by the optical system according to EP 2 164 028 rendering the code illegible.